The present invention generally relates to a wafer transfer chamber for use in a semiconductor processing apparatus and more particularly, relates to a wafer transfer chamber for a semiconductor process machine that can be operated with reduced particle contamination by utilizing a particle filter for isolating wafers in the transfer chamber and a method for operating the wafer transfer chamber equipped with such particle filter.
In the fabrication process for a semiconductor device, numerous processing steps must be performed on a semi-conducting substrate to form various circuits. The process may consist of as many as several hundred processing steps. Each processing step is executed in a process chamber such as an etcher, a physical vapor deposition chamber (PVD), a chemical vapor deposition chamber, etc.
In the vast majority of the processing steps, a special environment of either a high vacuum, a low vacuum, a gas plasma or other chemical environment must be provided for the process. For instance, in a PVD (or sputter) chamber, a high vacuum environment must first be provided that surrounds the wafer such that particles sputtered from a metal target can travel to and deposit on an exposed surface of the wafer. In other process chambers, such as in a plasma enhanced chemical vapor deposition chamber (PECVD), a plasma cloud of a reactant gas or gases is formed over a wafer positioned in a chamber such that deposition of a chemical substance can occur on the wafer. During any processing step, the wafer must also be kept in an extremely clean environment without the danger of being contaminated. The processing of a wafer therefore is normally conducted in a hermetically sealed environment that is completely isolated from the atmosphere. Numerous processing equipment has been provided for such purpose. One of such widely used cluster-type fabrication equipment is marketed by the Applied Materials Corporation of Santa Clara, Calif., i.e., the Centura(copyright) 5000 system.
In a typical Centura(copyright) 5000 cluster-type wafer handling system, as shown in FIG. 1, the basic system 10 consists of two independent vacuum cassette load-locks 12 and 14, a capacity for one to four independent process chambers (two of such chambers 16 and 18 are shown in FIG. 1), a capacity for two service chambers which includes an orienter 22, and a vacuum transfer chamber 20 which is isolated from vacuum cassette load-locks 12,14 and process chambers 16,18 by slit valves (not shown). The modular design of the basic system 10 is such that up to three high-temperature deposition chambers may be installed in the system. The basic system 10 can be used for fully automatic high-throughput processing of wafers by utilizing a magnetically coupled robot. The basic system 10 is further capable of transferring wafers which are maintained at a temperature as high as 700xc2x0 C. The basic system 10 also allows cross-chamber pressure equalization and through-the-wall factory installation. The vacuum pumps for the process chambers 16,18, the transfer chamber 20 and the cassette load-locks 12,14 are mounted at a remote location to prevent mechanical vibration from affecting the operation of the system.
The vacuum cassette load-locks 12,14, the process chambers 16,18 and the orienter 22 are bolted to the vacuum transfer chamber 20 and are self-aligned for ease of expansion or modification. Each of the process chambers 16,18 is capable of processing a single wafer for achieving wafer-to-wafer repeatability and control. The temperatures in the process chambers 16,18 are controlled in a closed-loop circuit for accuracy.
A plane view of the basic system 10 of FIG. 1 is shown in FIG. 2. In the basic wafer processing system 10 shown in FIGS. 1 and 2, the transporting of wafers between the various load-lock chambers 12,14, the process chambers 16,18 and the orienter 22 must be carefully conducted to avoid damages from occurring to the wafers. To accomplish such task, the wafer is transported by a wafer transfer system 24. The wafer transfer system 24 consists mainly of a robotic handler which handles all wafer transfers by a single, planar, two-axis, random access, cassette-to-cassette motion. A magnetically coupled robot permits good vacuum integrity and service without interrupting chamber integrity. The major component of the wafer transfer system 24 is a robot blade 28. The robot blade 28 permits high-temperature transfer of wafers without incurring contamination. A non-contact optical wafer centering process is also performed during the wafer transfer process. A constant flow of filtered inert gas such as nitrogen is used in the cassette load-locks 12,14 and the vacuum transfer chamber 20. A conventional robot blade 28 can be fabricated of a non-magnetic type metal such as aluminum.
One of the process chambers 16,18 is frequently used as an etch chamber for performing an etching process on a wafer. For instance, when he formation of alignment marks on the surface of a wafer is necessary, an etching process utilizing a corrosive gas is used for etching the marks (or holes) in the wafer surface. The surface layer etched may be a polysilicon layer. After the completion of the etching process, the robot lade 28 transfers the etched wafer from the etch chamber back into one of the load-lock chambers 12,14. When such direct transfer of wafers between an etch chamber and a load-lock chamber occurs, contaminating particles are were left on the surface of the wafer is carried into the load-lock chamber. While the number of contaminating particles left on a single wafer surface does not present a serious problem to load-lock chamber, the total number of particles carried on as many as 25 wafers stored in a wafer cassette situated in the load-lock chamber produces a cumulative effect an causes a serious contaminating problem.
FIGS. 3 and 4 are lane views and cross-sectional view of a load-lock chamber that has a different design when compared to the load-lock chamber of FIGS. 1 and 2. The different configuration of the load-lock chamber 30 which, similar to the load-lock chamber of FIG. 1, is equipped with a wafer cassette elevator 32. However, the wafer cassette elevator 32 is situated in load-lock chamber 30 which is part of the vacuum transfer chamber 20. The operation of the load-lock chamber 30 is similar to that shown previously. For instance, a wafer is first transferred from the load-lock chambers 12,14 to a wafer orienter 22 (not shown in FIG. 3) to locate the wafer flat side an the wafer center. The wafer is then transferred to a process chamber to carry out a process such as etching, physical vapor deposition or chemical vapor deposition. After the process is completed, the wafer may be transferred to a cool-down chamber for cooling if the process is conducted at a high temperature, otherwise, the wafer is transferred back into the load-lock chamber, i.e. into the wafer cassette. After all the wafers are processed, the wafer cassette elevator is lowered to its unload position and the chamber is vented to atmospheric pressure.
The venting of the chamber is conducted similar to the pumping process for the chamber with the wafer cassette situated on a platform of the elevator positioned in a lowermost position. During the pumping process for the load-lock chamber, as shown in FIG. 4, the process is carried out slowly, i.e. for a time duration of about 5 min. in order to avoid the creation of turbulent flow inside the load-lock chamber. This is to avoid the loosening of contaminating particles that may have attached to the chamber interior components from falling on the wafers. Similarly, during the venting process of the chamber interior, the venting must also be carried out slowly, i.e. for a time duration of about 5 min., in order to avoid turbulent flow in the chamber interior and the further distribution of contaminating particles on the wafer surfaces. Since the total volume of the chamber interior of a load-lock chamber is large when compared to the total volume of a wafer cassette, it is difficult to always maintain cleanliness of the chamber interior to avoid such contamination. The particle contamination problem exists even though the chamber interior is wet cleaned in approximately every two days. It is therefore desirable to provide an apparatus and a method for preventing particle contamination on wafers during either a pumping or a venting process of a load-lock chamber interior.
It is therefore an object of the present invention to provide a wafer transfer chamber such as a load-lock chamber that does not have the drawbacks or the shortcomings of the conventional wafer transfer chamber.
It is another object of the present invention to provide a wafer transfer chamber that has a reduced particle contamination problem.
It is a further object of the present invention to provide a wafer transfer chamber that has a reduced particle contamination problem during a pumping or venting process of the chamber interior.
It is another further object of the present invention to provide a wafer transfer chamber that has a reduced particle contamination problem by utilizing a particle filter in the chamber interior.
It is still another object of the present invention to provide a wafer transfer chamber that has a reduced particle contamination problem equipped with a particle filter for enclosing a wafer cassette during pumping or venting of the chamber interior.
It is yet another object of the present invention to provide a wafer transfer chamber that has a reduced particle contamination problem by utilizing a particle filter inside the chamber which is capable of filtering out any particles larger than 0.125 xcexcm diameter.
It is still another further object of the present invention to provide a method for preventing particle contamination in a wafer transfer chamber by positioning a wafer cassette inside a particle filter during a pumping or venting process for the chamber interior.
It is yet another further object of the present invention to provide a method for reducing particle contamination in a wafer transfer chamber by raising a cassette elevator to an uppermost position such that a wafer cassette is enclosed by a particle filter by engaging a top surface of a platform of the elevator to the particle filter during a pumping or venting process of the chamber interior.
In accordance with the present invention, a wafer transfer chamber that has reduced particle contamination problem and a method for pumping or venting a wafer transfer chamber with reduced particle contamination are provided.
In a preferred embodiment, a wafer transfer chamber that has reduced particle contamination problem can be provided which includes a chamber enclosure that has a top wall, a bottom wall and four sidewalls forming a vacuum tight cavity therein; a pumping means for evacuating the cavity to a pressure smaller than atmospheric pressure; a venting means for venting the cavity to atmospheric pressure; an elevator means that has a platform for holding a wafer cassette thereon and for moving upwardly or downwardly into a pumping/venting or unloading position, respectively; and a particle filter means that has a top panel and four side panels fabricated of a material capable of filtering out particles, the top panel being stationarily fastened to an interior surface of the top wall of the chamber enclosure while the four side panels forms an enclosure sealingly engaging a top surface of the platform when the platform is raised to an uppermost position by the elevator means during either a pumping or a venting operation.
In the wafer transfer chamber that has reduced particle contamination problem, the wafer transfer chamber may be a load-lock chamber for a semiconductor processing tool. The chamber may further include a pumping means for evacuating the cavity to a pressure lower than 100 mTorr, or an access door through one of the four sidewalls for transporting into/out of the chamber enclosure a wafer cassette. The particle filter means may have a top panel and four side panels fabricated of a material capable of filtering out particles larger than 0.25 xcexcm diameter, or preferably particles larger than 0.125 xcexcm diameter. The platform may further include a gasket member positioned on top and along a peripheral edge for sealingly engaging a bottom end of the four side panels of the particle filter means. The top panel and the four side panels of the particle filter means may be formed of a material fabricated of polymeric fibers.
The present invention is further directed to a method for preventing particle contamination in a wafer transfer chamber that can be carried out by the operating steps of providing a chamber enclosure that has a top wall, a bottom wall and four sidewalls forming a vacuum tight cavity therein, a pumping and a venting means for evacuating and venting the chamber cavity, an elevator means for holding a wafer cassette thereon and for moving upwardly or downwardly into a pumping/venting or unloading position, and a particle filter means that has a top panel and four side panels fabricated of a material capable of filtering out particles wherein the top panel is stationarily fastened to an interior surface of the top wall of the chamber enclosure; positioning a wafer cassette on a platform of the elevator means while the elevator means is positioned at a lowermost position and the chamber cavity at atmospheric pressure; elevating the elevator means to an uppermost position such that a top surface of the platform sealingly engages a bottom surface of the four side panels with the wafer cassette enclosed by the particle filter means; pumping the chamber cavity to a pressure smaller than atmospheric pressure; transferring wafers from the wafer cassette into process chamber by a wafer transfer robot until all wafers are processed; venting the chamber cavity to atmospheric pressure with the elevator means in the uppermost position and the wafer cassette enclosed in the particle filter means; and lowering the elevator means to a lowermost position for unloading the wafer cassette.
The method for reducing particle contamination in a wafer transfer chamber may further include the step of pumping the chamber cavity to a pressure lower than 100 mTorr. The method may further include the step of filtering out particles that have a diameter larger than 0.2 xcexcm by the particle filter means when the wafer cassette is enclosed by the particle filter means during the pumping step and the venting step, or the step of filtering out particles that have a diameter larger than 0.125 xcexcm by the particle filter means. The method may further include the step of mounting the wafer transfer chamber to a semiconductor cluster tool. The method may further include the step of transporting a wafer cassette into the chamber cavity through an access door provided in one of the four sidewalls of the chamber enclosure. The method may further include the step of fabricating the particle filter means with a material formed of polymeric fibers. The method may further include the step of transporting out of the chamber enclosure a wafer cassette after all wafers have been processed through an access door in one of the four sidewalls of the chamber enclosure.
The method for reducing particle contamination in a wafer transfer chamber may further include the step of providing a gasket member on a top surface of the platform for sealingly engaging a bottom surface of the four side panels of the particle filter means when the elevator means is moved into an uppermost position engaging the particle filter means. The method may further include the step of mounting the pumping means for evacuating the cavity through a bottom wall of the chamber enclosure, or the step of pumping the chamber cavity by the pumping means for a time period of at least 3 min., or the step of venting the chamber cavity to atmospheric pressure for a time period of at least 3 min.